The present invention relates to the production of oil and in particular to a centralizer for centralizing tubular structures and/or tools in a well pipe.
Oil is withdrawn from subterranean formations through a tubular production pipe formed by a string of tubing extending to the surface. The oil is lifted through the pipe by the action of a downhole pump actuated by a string of tubular structures including a plurality of sucker rods and/or at least one polished bar.
In recent years, directional and deviated wells have become very popular in many oil fields. Also, for heavy and extra heavy crude oil steam injection is used to improve oil production. In many of these wells, there is a polished bar that moves through a stuffing box. Frequently this polished bar as well as the piston stem associated with the subsurface or downhole pump fail because the reciprocating forces acting on the sucker rod string are not perfectly aligned and centralized with the stuffing box and/or the subsurface pump. As a result, undesirable radial forces are created which cause non-unifirm wear of the various components and lead to oil spills as well as premature pump failure.
Various devices for centralizing and guiding rods and/or tubular structures such as sucker rods within a tubular production pipe are known in the art. One type of device has a plurality of rollers for contacting the tubular pipe and maintaining a desired spacing between the tubular pipe and the reciprocating tubular structure or tool. U.S. Pat. Nos. 2,466,239 to Holcombe, 2,601,478 to Weir and 4,577,327 to Kinley et al. illustrate such devices.
Centralizing and guiding devices having fixed contact elements are also known in the art. U.S. Pat. No. 2,722,462 to Tschirley illustrates an elastomeric collar having a row of bumps or projections attached to a drill pipe. The projections help to maintain a desired separation between the pipe and the surrounding casing. U.S. Pat. No. 3,938,853 to Jurgens et al. illustrates a similar stabilizer device secured to a drill collar. The device comprises an inner sleeve and an external sleeve with a series of longitudinally extending helical ribs. The primary deficiency of using fixed contact elements such as these is their tendency to quickly wear out due to friction.
More recently, a centralizing device comprising a coupling device having a cylindrical body and a plurality of lenticular wheels positioned within slots in the body has been developed to overcome the frictional problem. To minimize scoring of the tubing wall, the wheel members are formed of a hard, non-abrasive material such as hard nylon. U.S. Pat. No. 4,621,690 to Klyne illustrates such a device.
Many of these devices when tested in wells having a temperature above 500.degree. F. have failed in giving high performance work life. Often, the non-metallic components of the devices are the weak links because they cannot withstand the critical conditions in the oil wells. In the wheeled devices, failure is also often the result of too few wheels being in contact with the production pipe tubing.
Accordingly, it is an object of the present invention to provide a centralizer which can be used with different oil well structures or tools to centralize the structures within the production pipe.
It is another object of the present invention to provide a centralizer as above which reduces frictional forces between the structures and the surrounding production pipe.
It is a further object of the present invention to provide a centralizer as above capable of withstanding typical oil well service conditions.
These and other objects and advantages will become more apparent from the following description and drawings.